The novel, divided into three books, tells the story of the quest for Captain Grant of the Britannia. The journey around the world forms a pretext to describe the flora, fauna and geography of numerous places to the targeted audience.
The first book, entitled 'South America' (published separately as The Mysterious Document) covers the events that occur after Lord and Lady Glenarvan of Scotland find a bottle cast into the ocean by Captain Grant himself after the Britannia is shipwrecked, and contact Mary and Robert, the young daughter and son of Captain Grant, through an announcement in a newspaper. Moved by the children's condition, Lord and Lady Glenarvan decide to launch a rescue expedition. The main difficulty is that the coordinates of the wreckage are mostly erased, and only the latitude (37 degrees) is known; thus, the expedition would have to circumnavigate the 37th parallel south. Remaining clues consist of a few words in three languages. They are re-interpreted several times throughout the novel to make various destinations seem likely. Lord Glenarvan makes it his quest to find Grant; together with his wife, Grant's children and the crew of his yacht the Duncan they set off for South America. An unexpected passenger in the form of French geographer Jacques Paganel (he missed his steamer to India by accidentally boarding on the Duncan) joins the search. They explore Patagonia, Tristan da Cunha Island, and other places in South America.
The second book, entitled 'Australia' (published separately as On the Track) is set in Australia There, they find a former quarter-master of the Britannia, Ayrton, who proposes to lead them to the site of the wreckage. However, Ayrton is a traitor, who was not present during the loss of the Britannia, but was abandoned in Australia after a failed attempt to seize control of the ship to practice piracy. He tries to take control of the Duncan for the same ends, and the second book finishes with the the Glenarvans, the Grant children, Paganel and some sailors in despair at the end of their voyage across Australia, in the belief that Ayrton has succeeded in his nefarious aims.
In the third book, entitled 'New Zealand' (published separately as Among the Cannibals) they sail on another ship to Auckland, New Zealand, from where they want to come back to Europe. When their ship is wrecked south of Auckland on the New Zealand coast, they're captured by a Maori tribe, but luckily manage to escape and board a ship that they discover, with their greatest surprise, to be the Duncan. Ayrton, made a prisoner, offers to trade his knowledge of Captain Grant in exchange for being abandoned on a desert island instead of being surrendered to the English authorities. The Duncan sets sail for the Tabor Island, which, out of sheer luck, turns out to be Captain Grant's shelter. They leave Ayrton in his place to live among the beasts and regain his humanity.